There is no clear compartmentalization between sociolinguistics and the sociology of language. The two fields of inquiry ask similar types of questions about the world around us, and use similar, sometimes overlapping methods when answering these questions.
Though there is a great deal of overlap between sociolinguistics and the sociology of language, important distinctions do exist. Sociolinguistics traditionally is more concerned with questions pertaining to how social factors become embedded within the language itself. Sociolinguistics seeks to understand how specific words and phrases came to exist in their current form, based on social factors such as race, class, and religion. Sociolinguistics is interested in the morphology of language, the pronunciation of words, spelling, punctuation, grammar, and usage.
The sociology of language has traditionally been concerned with more macro-type inquiries, such as how specific dialects come into existence, or how particular speech patterns influence the way the speaker is perceived. For example, how do words and language influence one's perceived expertise and social authority?
In general, the sociology of language takes on structural questions, inquiring into social systems, language systems, relationships, and social interactions. Sociolinguistics takes on descriptive and historical inquiries, aimed at giving us a better understanding of the social history of how specific language forms -- i.e. specific words or grammar patterns -- have come to exist in their current form.