IB/ipath: Make a few functions static

Make some functions that are only used in a single .c file static.  In
addition to being a cleanup, this shrinks the generated code.  On x86_64:

add/remove: 1/3 grow/shrink: 2/1 up/down: 4777/-4956 (-179)
function                                     old     new   delta
handle_errors                                  -    3994   +3994
__verbs_timer                                 42     710    +668
ipath_do_ruc_send                           2131    2246    +115
ipath_no_bufs_available                      136       -    -136
ipath_disarm_senderrbufs                     639       -    -639
ipath_ib_timer                               658       -    -658
ipath_intr                                  5878    2355   -3523

Signed-off-by: Roland Dreier <rolandd@cisco.com>