protocol/sip: Make comparison specific
protocol/sip: Make comparison specific

parser_sip.c:906:6: warning:
logical not is only applied to the left hand side of this comparison
[-Wlogical-not-parentheses]
if (!psip->fromURI.len == 0
    ^                  ~~

sipcapture/captagent,sipcapture/captagent,sipcapture/captagent