Move sb_state to the beginning of structure, above sb_startzero member.

Move sb_state to the beginning of structure, above sb_startzero member.
sb_state shouldn't be erased, when socket buffer is flushed by sorflush().

When sb_state was bzero'ed, a recently set SBS_CANTRCVMORE flag was cleared.
If a socket was shutdown(SHUT_RD), a subsequent read() would block on it.

Reported by:	Ed Maste, Gerrit Nagelhout
Reviewed by:	rwatson