phonet: sparse annotations of protocol, remove forward declaration

net/phonet/af_phonet.c:38:36: error: marked inline, but without a definition
net/phonet/pep-gprs.c:63:10: warning: incorrect type in return expression (different base types)
net/phonet/pep-gprs.c:63:10:    expected int
net/phonet/pep-gprs.c:63:10:    got restricted __be16 [usertype] <noident>
net/phonet/pep-gprs.c:65:10: warning: incorrect type in return expression (different base types)
net/phonet/pep-gprs.c:65:10:    expected int
net/phonet/pep-gprs.c:65:10:    got restricted __be16 [usertype] <noident>
net/phonet/pep-gprs.c:124:16: warning: incorrect type in assignment (different base types)
net/phonet/pep-gprs.c:124:16:    expected restricted __be16 [usertype] protocol
net/phonet/pep-gprs.c:124:16:    got unsigned short [unsigned] [usertype] protocol

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>