The marriage of Jane to Mr. Bingley can actually be seen as both a challenge to and reinforcement of regency England social conventions, or really even as neither of the above. The true irony of the match that Austen is pointing out actually goes beyond established social conventions. The true irony is that the match was objected to, even though there really was very little foundation for the objections. Both Bingley's sisters as well as other characters like Darcy and Lady Catherine de Bourgh make it very clear that they object to the match and think that it is "beneath" Bingley.
Bingley's sisters make their opinion well known when we witness them making snide remarks behind Jane's back about the Bennet family's working class relations, such as Mr. Philips, who is an attorney in Meryton, and Mr. Gardiner, who is in trade and lives in Cheapside, London, the business district. They laugh at her "heartily," and even Darcy remarks that such connections "must very materially lessen their chances of marrying" well (Ch. 8). Later, we learn in Darcy's letter that both he and Bingley's sisters dissuaded Bingley from the marriage due to Jane's family connections as well as due to the fact that they thought she did not really love him.
However, the irony in all of these objections to the match is that, in terms of class, Jane is marrying a man who, while a great deal wealthier than she is, is actually socially beneath her. During Austen's time period, England was seeing a rise in the wealth of the working class. Some members of the working class were becoming wealthy enough to purchase their own estates and rub shoulders with the landed gentry. Austen very intentionally points out early on in the book that Bingley is actually a member of this new rising working class, the middle class. Austen establishes that Bingley's father made the Bingley fortune through trade and left it to Bingley to purchase a family estate. Bingley wants to, but he is so content renting a "good house" like Netherfield that he might just "leave the next generation to purchase" (Ch. 4). Hence, Bingley is actually a wealthy member of the working class, and without an estate, he does not yet qualify as a member of the landed gentry. Jane, on the other hand, is the daughter of Mr. Bennet, a gentleman who does own an estate, earning his income from the tenants working his estate. Therefore Jane actually is a member of the landed gentry and has married socially beneath her by marrying Bingley, even if she has working class relations on her mother's side of the family. However, her family certainly considers the match an advantage due to Bingley's wealth.
Therefore, since the Bennet family gained wealth and security through Jane's marriage to Bingley, on the one hand, the marriage reinforced accepted social conventions of regency England, such as marrying for financial gain. But on the other hand, since Jane actually did marry beneath her class, the marriage did challenge social conventions, but not really very much. Mixing social classes through marriage, though looked down upon, was something commonly done. Even Mr. Bennet married beneath him when he married Mrs. Bennet who came from the working class. Therefore, the marriage never really entirely reinforces nor challenges all social conventions. Instead, the true irony of the match that Austen is pointing out is that the marriage was needlessly looked down upon.