MFC r262868

Only use -lpthread for unix_seqpacket_test, not for all test programs.

MFC r262894

kern/Makefile
        Set WARNS=5 for all files in this directory
kern/unix_seqpacket_test.c
	Fix compiler warnings.  Most were benign, but rcvbuf_oversized
	wasn't working as intended because I forgot to set the buffer sizes.
MFC 262999
Fixed MSI interrupt allocation and handling.
Fixed a DMA mapping leak that occurs when defragmenting packet chains.

Approved by:	davidch (mentor)