RDMA/nes: Make unnecessarily global functions static

This allows the compiler to do a bit better; on my x86-64 build:

add/remove: 0/2 grow/shrink: 1/0 up/down: 2288/-2365 (-77)
function                                     old     new   delta
nes_init_phy                                 273    2561   +2288
nes_init_1g_phy                              469       -    -469
nes_init_2025_phy                           1896       -   -1896

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