sockets: return EMSGSIZE if control part of message is too large

Specification doesn't list an explicit error code for the control
size specified by msg_control being too large. But it does list
EMSGSIZE as error code for "message is too large to be sent all at
once (as the socket requires)". It also lists EINVAL as code for
the "The sum of the iov_len values overflows an ssize_t." Given
how generic and uninformative EINVAL is, the EMSGSIZE is more
appropriate.

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sendmsg.html

Reviewed by: markj
Differential revision: https://reviews.freebsd.org/D35316