MFC r241726:

 Move UMA socket zone initialization from uipc_domain.c to uipc_socket.c
 into one place next to its other related functions to avoid confusion.

MFC r241729:

 Move socket UMA zone initialization functionality together into
 one place.

MFC r241779:

 Tidy up somaxconn (accept queue limit) and related functions
 and move it together into one place.